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A bar of olive soap weighs about a hundred and ten grams, and on its wrapper sits a short paragraph of small type beginning with the word Ingredients. That paragraph has its own grammar: order, thresholds, Latin names, the word Parfum, a few chemical names at the end. This piece reads an INCI ingredient list from the top down, the way one reads a sentence.

One soap label, ten lines of type

Lê Mai's Olive Soap is a cold process bar in which olive oil makes up more than seventy percent of the formula, alongside neem seed oil, shea butter, cocoa butter and an essential oil blend, twelve ingredients in all. Written in words, that is a description. Written in INCI, it is a list with rules.

On the ingredient list, olive oil is not called olive oil. It is Olea Europaea Fruit Oil: genus, species, the part of the plant, and the form of the material. Shea butter is Butyrospermum Parkii Butter. Cocoa butter is Theobroma Cacao Seed Butter. Each name is a precise address, pointing to one plant and one part of it.

The style looks dry, but it solves a real problem. One oil can carry dozens of trade names and local names; the single word olive can be translated many ways in many languages. A list written in INCI reads the same in Hanoi, in Paris and in Tokyo, without translation.

INCI: one name for every country

INCI stands for International Nomenclature of Cosmetic Ingredients. The rules of the naming system were established in 1973 by the United States cosmetics trade association, now the Personal Care Products Council. Since then each material has been given one name, and regulators in many places reuse the system.

The European Union wrote the principle of common names into law. Regulation 1223/2009 requires the ingredient list to use the common ingredient names of the European Commission's glossary, which is based on INCI. According to the library's glossary, essential oils are listed by the Latin name of the plant with part and form, for example Lavandula Angustifolia Oil for lavender oil.

INCI grammar has a few easy conventions. Plant names keep their Latin Linnaean form. Water is written Aqua. A fragrance blend is written Parfum. Chemicals keep their English chemical names, such as Glycerin or Sodium Hydroxide. Once these few conventions are familiar, most cosmetic labels become readable.

Order by amount and the one percent line

An ingredient list is not a random list. Under Article 19 of Regulation 1223/2009, ingredients are listed in descending order of weight at the time they are added to the formula. The largest comes first. For an olive soap in which olive oil is more than seventy percent of the oils, the name of the olive oil, or of its soap salt, belongs at the head of the list.

A second rule changes how the end of the list is read. Ingredients below one percent may be listed in any order, after those above one percent. The second half of an ingredient list is therefore often a zone without rank: an extract placed before a preservative does not mean there is more of it.

Soap adds its own detail. Soap forms when oils react with sodium hydroxide, so a label may show one of two styles: the starting oils together with Sodium Hydroxide, or the name of the resulting salt, such as Sodium Olivate. Glycerin appears because it is produced by the saponification itself. Both styles describe the same bar, at two different moments of its life.

The law also says what is not an ingredient: impurities in raw materials, and technical aids used during processing but absent from the final product. An ingredient list records what was deliberately put in, not a chemical analysis of the finished item.

Essential oils written in Latin

For essential oils, the Latin name carries more information than the common one. Melaleuca Alternifolia Leaf Oil says this is tea tree, the species alternifolia, from the leaf. Citrus Grandis Peel Oil says the oil comes from pomelo peel. A word such as Leaf, Peel, Seed, Wood or Root is part of the identity, because one plant can give very different oils from different parts.

But INCI has limits. The Latin name does not say whether an oil was cold pressed or distilled, even though for citrus that is the decisive difference between an oil that can be phototoxic and one that is not. It does not give the chemotype, the chemical profile of a plant population. It does not give the growing region or the lot. That information lives on each oil's page in the library, not on the label.

Carrier oils follow the same logic. The library's vegetable oils page lists carrier oils and butters, and most have INCI names on the same pattern: genus, species, part, form. A reader familiar with a few dozen common Latin names will recognise most plant based materials on a soap or body oil label.

Parfum and allergens

The word Parfum on an ingredient list is a collective word. Under European labelling law and in the library's glossary, a fragrance blend may be declared under the single word Parfum, or Aroma for a flavour. Dozens of aromatic materials can sit behind one word. This is how the law protects a perfumer's formula.

There is an exception, and it explains why so many lists end with names such as Linalool, Limonene, Citral, Geraniol. A group of fragrance substances classed as contact allergens must be named individually above a threshold: 0.001 percent in leave-on products, 0.01 percent in rinse-off products. The older list held 26 substances; Regulation 2023/1545 extends it, and according to the library, new products placed on the European market must comply from 31 July 2026.

The threshold is so low that nearly every product containing essential oils reaches it. The library's linalool page records lavender oil at about 20 to 38 percent linalool. A body oil with 1 percent lavender holds about 0.2 to 0.38 percent linalool, hundreds of times the 0.001 line. Likewise, limonene makes up most of a citrus peel oil, so a soap scented with orange almost certainly has to name it.

The word Linalool at the end of an essential oil soap label therefore does not mean someone added a synthetic chemical. It usually means the essential oil brought that molecule with it, and the law requires it to be named. A natural essential oil still contains allergens; a plant origin does not change that.

What the label does not say

An ingredient list answers the question what, not how much. Beyond the order, the label gives no percentages. It does not say whether an essential oil is 0.5 or 3 percent of the product, although for many oils that figure is exactly what decides whether a product sits within safe limits. The library's safety page gives dermal limits as percentages for each oil, and those figures cannot be read from a label.

The label also says nothing about freshness. Pure linalool and limonene seldom cause reactions, but according to the library their oxidised forms, the hydroperoxides, are far more sensitising. The same word Limonene can sit on a new bottle and on one opened two years ago. Storage and shelf life are information that lives outside the ingredient list.

And the label says nothing about the person using it. An allergen is named so that people who already know they react to it can avoid it. For someone who has never reacted, the name is simply information. Reading the grammar of a label does not replace testing a small amount on skin, or asking a dermatologist when there is a history of allergy. The piece on the names at the end of an ingredient list reads the allergen list more closely.

An ingredient list is a sentence written by weight.

The top speaks about material. The end speaks about law.

What is left unwritten is part of the label too.